Change the HTTP header field names to lowercase

sdk/lib/io/http_impl.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart.io;
 
 class _HttpIncoming
     extends Stream<List<int>> implements StreamSink<List<int>> {
   final int _transferLength;
   final Completer _dataCompleter = new Completer();
@@ skipping 152 matching lines @@
                       _HttpClientRequest this._httpRequest,
                       _HttpClient this._httpClient)
       : super(_incoming);
 
   int get statusCode => _incoming.statusCode;
   String get reasonPhrase => _incoming.reasonPhrase;
 
   List<Cookie> get cookies {
     if (_cookies != null) return _cookies;
     _cookies = new List<Cookie>();
-    List<String> values = headers["set-cookie"];
+    List<String> values = headers[HttpHeaders.SET_COOKIE];
     if (values != null) {
       values.forEach((value) {
         _cookies.add(new Cookie.fromSetCookieValue(value));
       });
     }
     return _cookies;
   }
 
   bool get isRedirect {
     if (_httpRequest.method == "GET" || _httpRequest.method == "HEAD") {
@@ skipping 275 matching lines @@
           break;
         }
       }
       if (!found) {
         cookies.add(new Cookie(_DART_SESSION_ID, session.id)..httpOnly = true);
       }
     }
     // Add all the cookies set to the headers.
     if (_cookies != null) {
       _cookies.forEach((cookie) {
-        headers.add("set-cookie", cookie);
+        headers.add(HttpHeaders.SET_COOKIE, cookie);
       });
     }
 
     headers._finalize();
 
     // Write headers.
     headers._write(this);
     writeCRLF();
   }
 
@@ skipping 170 matching lines @@
 
     // Add the cookies to the headers.
     if (!cookies.isEmpty) {
       StringBuffer sb = new StringBuffer();
       for (int i = 0; i < cookies.length; i++) {
         if (i > 0) sb.add("; ");
         sb.add(cookies[i].name);
         sb.add("=");
         sb.add(cookies[i].value);
       }
-      headers.add("cookie", sb.toString());
+      headers.add(HttpHeaders.COOKIE, sb.toString());
     }
 
     headers._finalize();
 
     // Write headers.
     headers._write(this);
     writeCRLF();
   }
 }
 
@@ skipping 985 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }